Stovepipe, West 12 Shopping Centre, London<br/>Over There, Royal Court Downstairs, London<br/>Berlin Hanover Express, Hampstead, London

Planning some retail therapy? Think again. If you wander into the West 12 shopping mall in Shepherd's Bush, you may be surprised to find yourself directed down into its vast concrete basement. In this normally deserted space, a compelling promenade piece called Stovepipe unfolds, by the young dramatist Adam Brace.

Audience members are initially treated like business conference delegates, visiting the Middle East. "Welcome to Project Rebuild Iraq!" chirp the smart-suited reps, handing out security passes and ushering everyone towards a specially created lecture hall and exhibition space – where promotional videos envisage sparkly new cities springing from the rubble.

Next thing you know, sirens are wailing and the keynote speaker, André – who runs a military security firm – is hurled to the ground by his armed bodyguard, Shaun Dooley's Alan. From here we vault backwards in time to see Alan joining André's private corps along with his ex-British Army mates, Grif and Eddy. One of them gets firebombed in an ill-equipped convoy and the other goes Awol, or may have been kidnapped. Alan attempts to track him down.

Staged with imaginative daring by Michael Longhurst, a director who will surely go far, Stovepipe is like Gregory Burke's Black Watch crossed with the epic theatrical installations of Punchdrunk. The basement is a maze: a hotel bedroom behind drapes suddenly opens into an airy atrium, then jostling streets, a shadowy building site patrolled by yelling guards, hushed HQ offices and a funeral chapel. Sound effects (by Steve Mayo) snap the mood between calm and panic: a muezzin's mellifluous call to prayer; a frenzied revving of engines and helicopter blades.

Brace will, doubtless, be headhunted to write for TV and the big screen, though the narrative structuring here has experimental adventurousness. The dialogue is exhilaratingly convincing, inspired and informed by Brace's interviews with private military company employees in the Middle East. There's a disturbing ring of truth about the two jumpy guards who shoot a curfew-breaking local and, on finding only fizzing soda cans stuffed inside his coat, conduct the cola-taste test – either callously or in a state of shock.

Granted, the evening gets off to a slightly slow start but it soon becomes gripping. The cast take multiple roles, changing accents and costumes at speed, and what comes across strongly is the ex-servicemen's anger at raw deals they've felt compelled to accept.

Dooley's Alan exudes burly steadiness, and brooding rage. Niall MacGregor shines as the laddish Scot, Eddy, drunkenly larking but with flaring bitterness. Sargon Yelda charms as long-suffering translator Saad, who teasingly feigns to admire Mr Bean films and resists André's coldly domineering wife (Eleanor Matsuura).

All in all, a highly impressive transfer from Suffolk's talent-nurturing HighTide drama festival, with backing from the NT and Bush Theatre. Which makes one wonder all the more at the Royal Court coming up with nothing better than Over There, Mark Ravenhill's dire latest effort – part of the venue's Off the Wall season about the legacy of contemporary Germany.

The most enticing aspect of this premiere, co-directed by Ravenhill and Ramin Gray, is that it's performed by real-life twins. Actors Harry and Luke Treadaway play siblings Franz and Karl, separated in childhood when their mother escaped to the West – leaving Karl behind with their socialist father.

When the Berlin Wall falls, the Eastern twin is hungry for the other's lifestyle. They have some telepathic sympathy, repeatedly speaking in synch, but the Western brother gets cold feet when the other wants to share his place in the world, in a matching suit.

The Treadaways are certainly game, stripping to their Y-fronts for a flurry of downstage-centre masturbation. Ideologically messed-up, Luke's Karl spirals into a breakdown, caking himself with gunky capitalist-brand foodstuffs. Harry's Franz – a consumer to the last – adds ketchup and feeds, like a vampire, on the other's dying body.

I presume this is meant to be shocking, in-yer-face, and an avant-garde sociopolitical parable. In truth, it's a bore; Ravenhill's writing seems to be regressing. "Now," cries Franz, "we are one!" Given the puerility of all this, one can be forgiven for thinking of A A Milne's children's verses, Now We are Six.

Berlin Hanover Express is, by comparison, only mildly disappointing. A theatrical debut for veteran TV scriptwriter Ian Kennedy Martin (devisor of The Sweeney), this fictional drama is set in the Irish diplomatic mission in Hitler's capital, late 1942. A senior and a junior diplomat – Sean Campion's Mallin and Owen McDonnell's rakish O'Kane – find themselves increasingly at odds over De Valera's war "neutrality". Holocaust evidence mounts and a rabid Nazi, Peter Moreton's Kollvitz, is menacingly interested in the diplomats' menial helper, Isla Carter's nervous Christe.

Campion's punctiliousness is ultimately chilling but his colleague is wearisomely verbose. Director Michael Rudman covers scene changes with oddly piecemeal newsreels, and Carter's enforced strip feels uncomfortably like collective voyeurism. Missable.

'Stovepipe' (020-7452 3000) to 26 Apr; 'Over There' (020-7565 5000) to 21 Mar; 'Berlin Hanover Express' (020-7722 9301) to 4 Apr